There are often instances when a person or object cannot be found, such as a missing person or pet; a stolen automobile; and objects lost en route during shipping, among others. This can be especially true if the person or object is located in a building or underground. Additionally, in other situations, it is difficult to identify areas with overcrowding and traffic congestion during large gatherings and events, potentially preventing resources from being deployed where they are needed most for crowd and traffic control. In still other situations, it is difficult to detect and monitor the presence of particular substances or environmental conditions at a given location. Further, some systems for locating persons or objects use devices that are easily detected and removed, thereby thwarting recovery efforts.